Work machines, including on-highway trucks and other types of heavy machinery, are used for a variety of tasks. These work machines may include a transmission coupled to an engine such as, for example, a diesel engine, a gasoline engine, or a natural gas engine that provides the power to complete these tasks. The transmission may be a mechanical, hydro-mechanical, hydraulic, or electric transmission that transmits engine power to a traction device. A power load placed on the transmission by the traction device is transmitted to the engine. Power load changes, either requiring additional power or less power, may cause the engine to deviate from a desired operating range. Deviations from the desired speed range may result in poor efficiency, less production, increased wear on the engine, and operator dissatisfaction.
Work machines may include a flywheel to minimize the variations in engine speed caused by a change in the power load. The magnitude of the speed changes may be minimized by increasing the inertia of the flywheel. However, as flywheel inertia increases, responsiveness of the engine decreases. A conventional flywheel may be inefficient at providing a balance between minimizing engine speed fluctuations and allowing the engine to respond quickly to desired power changes. A range of flywheel sizes may be provided for a particular engine application to allow selection of flywheel size based on expected load changes. Unfortunately, this may result in increased parts, tooling, and production cost.
In an attempt to provide a flywheel offering improved response to a wider range of load changes, at least one variable inertial mass flywheel has been proposed. For example, U.S. Pat. No. 5,007,303 (the '303 patent) issued to Okuzumi on Apr. 16, 1991, describes a variable inertial mass flywheel having a main flywheel member coupled to an engine crankshaft and a sub-flywheel member separated from the main flywheel member by electrorheological fluid. The viscosity of an electrorheological fluid is proportional to the intensity of an electric field applied to the fluid. During power load fluctuations, the intensity of the electric field is changed to change the viscosity of the electrorheological fluid. As a result, the change in viscosity increases or decreases friction between the main flywheel and the sub-flywheel. During accelerations or decelerations, the intensity of the field is set low to minimize friction between the main flywheel and the sub-flywheel, thereby creating a low inertia flywheel that may respond quickly. During power load changes of high magnitude, the intensity of the field is set high to increase friction between the main flywheel and the sub-flywheel, thereby creating a high inertia flywheel that may offset the high magnitude changes in power load.
While, the variable inertial mass flywheel of the '303 patent may offer an improved response to a wider range of load changes, as compared to traditional fixed-mass flywheels, the flywheel of the '303 patent may be problematic. For example, the variable inertial mass flywheel may not efficiently use and/or dissipate the energy absorbed by the flywheel.
The present invention is directed to overcoming one or more of the problems set forth above.